1. Field of the Invention
The present invention relates to an optical semiconductor device and a method for manufacturing the same.
2. Description of the Related Art
In response to the development of a high-intensity optical semiconductor element that emits blue light, there has been commercialized an optical semiconductor device that emits white light by using an optical semiconductor element that emits blue light and a phosphor capable of wavelength conversion from blue light into yellow light. Such an optical semiconductor device that emits white light has characteristics of: being small in size; emitting high-intensity light relative to a supplied power amount; having a long life; and using no toxic substance such as mercury. These characteristics allow the optical semiconductor device to be increasingly used in various fields such as application to an under-button light source or a flash light source for portable phone and application to an interior light source and an exterior light source for vehicle.
In terms of total flux relative to a supplied power amount, an optical semiconductor device using blue LEDs currently has an efficiency of 150 lm/W, which is larger than those of conventional light sources such as an incandescent light bulb (15 lm/W to 20 lm/W) and a fluorescent lamp (60 lm/W to 90 lm/W). However, in terms of cost required for one lm, the optical semiconductor device has a problem of requiring cost more than ten times higher than the conventional light sources which require 0.1 yen/lm to 0.2 yen/lm. As a measure to reduce the cost, there has been studied a structure of an optical semiconductor device allowing cost reduction while enhancing the luminous efficiency of an element therein.
The most general optical semiconductor device that has been commercialized has a structure including: an optical semiconductor element that emits blue light; an Ag-plated Cu frame formed of a white thermoplastic resin by molding, and used as a wiring board; a connection material for connecting the optical semiconductor element and the frame; a gold wire through which a current flows between the frame and a top surface electrode of the optical semiconductor element; and a silicone resin mixed with phosphor particles for wavelength conversion from blue light into yellow light and sealing in the optical semiconductor element (see JP-A No. 2000-183407 (KOKAI), for example).
In manufacturing this optical semiconductor device, a white thermoplastic resin is firstly formed into the Ag-plated Cu frame by molding. Then, a connection resin is applied onto a portion, on which the optical semiconductor element is to be mounted, of the frame. Thereafter, the optical semiconductor element is mounted on the portion, and the connection resin is hardened by heating in an oven. Thereby, the optical semiconductor element is connected to the frame. Then, by using a wire bonder, the electrode formed on the chip top surface of the optical semiconductor element is connected to the frame with an Au wire. Thereafter, a silicone resin with a phosphor concentration adjusted to allow the optical semiconductor device to emit white light is applied, by a dispense technique, around the portion in which the optical semiconductor element is mounted, and then hardened by heating. Lastly, a product portion including the optical semiconductor element is cut off, and the frame used as an exterior electrode is finished by a forming process. Thereby, the optical semiconductor device is completed.
As described above, a conventional optical semiconductor device is manufactured by incorporating a blue light semiconductor element in a structure of an optical semiconductor device that, in most cases, has been commercialized using an optical semiconductor element that emits light having a wavelength of 500 nm or more. The optical semiconductor device that emits such long-wavelength light has a high directivity and has thus been applied to devices for vehicle, display panels, amusement machines and the like.
Such a conventional optical semiconductor device manufactured as above has a problem of having a shorter life for reasons, such as that blue light, which has a short wavelength and a high intensity, discolors a reflector resin having benzene ring. In addition, an optical semiconductor device that emits white light commercialized in response to the development of a high-intensity optical semiconductor element that emits blue light has been increasingly applied to lighting apparatuses as well as conventionally-applied apparatuses such as devices for vehicle and display panels. With this trend, cost reduction of the optical semiconductor device has been indispensably required. However, the conventional structure of an optical semiconductor device only allows limited cost reduction, and thus the structure and the manufacturing process of the optical semiconductor device has been required to be reconsidered.
In addition, when an optical semiconductor device is applied to a lighting apparatus, a light source therein cannot be formed of a single optical semiconductor device. Accordingly, in order to replace a general lighting apparatus, such as a fluorescent lamp, with an apparatus using an optical semiconductor device that emits white light, the apparatus needs to include multiple optical semiconductor devices. In this case, to eliminate defects such as nonuniform intensity in a light-emitting surface, a large number of small optical semiconductor devices need to be mounted on a wiring board. Accordingly, the size reduction of the optical semiconductor device has also been required.